This invention relates to connector or nailing plates, and more particularly to connector plates having a plurality of teeth projecting therefrom for securing together adjacent wood members to form a wood structure (e.g., for securing together the web and chord members of a roof or floor truss).
The teeth of the connector plate must be sufficiently strong to withstand forces necessary to drive or force them into the wood without bending over or buckling. When the teeth are imbedded in the wood, the connector plate must be sufficiently strong to hold adjacent wood members securely together so as to withstand the substantial tension, compression, shear and/or torsion loads to which the joint is subjected during fabrication of the structure, transportation of the wood structure to the building site and erection of the building (these fabrication, transportation and erection loads being generally referred to as handling loads), and during the life of the building with an adequate margin of safety to accommodate overload conditions.
Conventionally, connector plates are pressed into the wood members either by a powerful fluid-operated press (e.g., a C-shaped hydraulic press or the like) or by a gantry roller press. It is generally believed that pressing the connector plates into the wood members with a hydraulic press results in superior joints because only perpendicular forces are applied to the connector plate and to the wood members by the press. Thus, the plates are cleanly driven into the wood members and the wood members remain in their desired positions relative to one another during the pressing operation. By using a large gantry roller press to drive the connector plates into the wood members, a plurality of connector plates may be at least partially driven into the wood members during each pass of the gantry roller press thus facilitating increased production rates. However, as the roller press contacts and moves across each connector plate, the plate may tend to conform to the roller surface. That is, the plate may tend to curl or curve upwardly, particularly at the end thereof in advance of the roller and substantial lateral forces may be applied to the teeth of the connector plate and to the wood members by the roller. Thus, as the teeth are unevenly forced into the wood members by the roller press, the teeth may be inclined somewhat from the vertical so that the teeth may be bent flat or the wood members may be excessively torn or split. Such bending of the teeth may significantly weaken the joint and may not readily be found upon visual inspection of the joint. Reference may be made to U.S. Pat. No. 3,479,920 which shows a connector plate especially designed for use with gantry roller presses.
More generally, the strength of the connector plate (referred to as the plate rating) is conventionally evaluated by determining the ability of the connector plate teeth to resist withdrawal from the wood member and to resist movement through the wood member when two wood members joined together in end-to-end abutting relation by the connector plates are subjected to axial tension loading. However, in practice, connector plates joining the web and chord members of a truss may have loads other than axial tension loads applied thereto. These nonaxial loads may tend to cause the plate to rotate relative to the wood members or to tear or split the wood members thus weakening the joint. Most often the strength and load-holding capacity of the tooth is greatest when the face of the tooth is at right angles to the load. Thus conventional plates have a high load-holding capacity when the load is applied in one direction (e.g., along a line perpendicular to the lateral plane of the teeth of the connector), but may have a substantially lower load-holding capacity when the load is applied in another direction (e.g., along a line substantially parallel to the lateral plane of the teeth). If the load is applied parallel to the lateral plane of the teeth, the teeth present a relatively narrow edge or area to the load and the wood in contact with the narrow edges or faces of the teeth may be subjected to such high loading per unit area that the wood may fail.
Reference may be made to such U.S. Pat. Nos. as 3,347,126 and 3,633,454 and to the above mentioned U.S. Pat. No. 3,479,920 which disclose connector plates broadly similar to the connector plate of the present invention.